Loud-speaker



Oct. 15, 1929- THOMAS 1,731,799

LOUD SPEAKER Filed March 12, 192'? .2 Sheets-Sheet 1 INVENTOR Oct. 15, 1929. A. A. THOMAS 31,731,799

LOUD SPEAKER Filed March 12, 1927 2 Sheets-Sheet 2 W W I'W W T /3 6 /z\ W; 1 H i /Z 1 1 L /5 V6 L/L i I ,V

Ll Ll U INVENTOR Patented Oct. '15, 1929 PATENT OFFICE monrna rnouaaornnw YORK, 11. Y.

rotm-srmxna Application file March 12, 1827. Serial No. 174,724.

Thepresent invention relates to electric sound-reproducing devices, usually called loudspeakers, such as are used in radio reception, phonographic reproduction and telephone receiving systems. The object of my invention is to provide a hornless loudspeaker of compact construction and capable of giving a reproduction of great volume and fidelity over the entire musical scale. 1 I

m --In a preferred embodiment I em y a plurality of loudspeaking diaphragms avlng different natural frequencies. As a general rule, two diaphragms are suific1ent,'one for accentuating the higher frequencies and the M other for accentuating the lower frequencies, and these diaphragms are supported in a frame of novel construction. This frame is of trihedral shape, and, the diaphragms are mounted on the two front faces or anels.

W The third or rear face of the frame pre erably consists of (or is otherwiseprovided with) a sounding board. The faces of the tr1- hedral frame form an open sound chamber for confining a column of air. The die- 2. phragmsare so mounted that on the front 51 de they are directly open to the outer air, and on the reverse side they are ex osed to the column of airjn the sound cham er'. Consequently, when the diaphr'agms arevlbrated by means of electromagnetic driving un ts,

- the inner column of air andthe soundlng board are set in vibration to. amplify the reproduction. The movements of the sounding board may be utilized to generate electrlc impulses for augmenting the electromagnetic action of the driving units, whereby the final reproduction is greatly amplified.

The foregoing and other features and advantages of my invention will be clear to those skilled in the art from a detailed description of the accompanying drawings, in wh1ch-- Fig. 1 shows a perspective view of a preferred form of loudspeaker constructed in accordance with my invention;

. Fig. 2 is a plan view of Fig. 1;

. Fig.3 represents an enlarged transverse section approximately on line of Fig. 1, certain portions being broken awayfor lack 5 of space;

wall of t e frame;

Fig. 4.-; shows a rear view of a front panel of the trihedral supporting frame;

Fig. 5 is arear view of Fig. 1, showing the mountin of the sounding board on the back Fig. 6 is a detached view of the currentgoenggating unit controlled by the sounding Fig. 7 is a cross-section on line 77 of Fig. 6;

Fig. 8 is an inside view of the electromagnetic driving unit for the diaphragms; and Fig. 9 is a diagram of the circuit connections for controlling the operation of the driving units. 7 The trihedral frame F consists of a pair of front panels or faces 10 and a rear panel 11. In the present instance the rear panel is not solid, as well it may be, but is in skeleton or spider form to provide rigid arms 12, which 7 terminate in a cylindrical head 13. The arms 12 support a sounding board 14, which is secured in position by screws 15 or in any other practical way. Insulating sleeves or pegs 16 hold the sounding board spaced from 7 the wall 11, so that it may vibrate as freely as ggssible in the sound chamber 17 formed wit "n the hollow supporting frame F.

The front walls 10 of frame F are provided with openings 18 in which are mounted a pair of loud-speaking diaphragms 19 and 20, which may conveniently be of the so-called cone type, either circular or elliptical. In the present construction the diaphragms are of elliptical shape, so that the maximum acoustic surface may be accommodated within the rectangular area of the supporting panels 10. The diaphragms are mounted on the supporting frame in any practical wa as by means of clamping rings 21, which t into correspondingly shaped recesses 22 on panels 10. Screws 23 or other fastening devices hold the rings 21 in clamping position.

The diaphragms 19 and 20 are preferably constructed to accentuate different bands of frequencies for the proper reproduction of the that diaphragm 19 is intended to operate most efliciently on the higher bands of freuencies, and that diaphragm 26 accentuates t 0 lower frequencies, there being suflicient overlapping between these frequencies to reroduce the middle r 'ster with the same egree of efliciency. one' diaphragms are usually made of aper, but' other materialswaves produced by the vibrating air column reach the outer air, they augment thesound waves generated by the outerfaces "of the diaphragms, thus increasing the volume of reproduction. The sound chamber 17 is so designed that sound waves produced by diaphragms 19- and 20 cause vibration of the soundin board 14,- as previously "explained.

iaphragms 19 and 20 are operated The " by electromagnetic driving units indicated as a whole by E. .These units are rigidly supported in a head 24 which may be integral with arms 25-formed on panel 10. The construction of the electromagnetic units E is clearly shown in Figs. 3 and 8. As these units are alike, a description of one will be sufiicient. The operative arts of the unit are housed in a casing26 a apted to fit snugly in the supporting head 24, to which it is secured by screws 27 or otherwise. On the base plate 28 of the unit is mounted a permanent steel magnet 29, l which may be stamped out of sheet steel as a single member, or it may be composed of two u-shaped magnets secured in contact with each other attheir like poles. By making the magnet.

structure elongated, somewhat in the shape of an elli se, an increased length of magnetic path is o tained, thereby adding to the life and efliciency of the magnet. Insulating. pads or blocks 30 may be used to hold the magnet spaced from the base. To the polar ends of magnet 29 are secured L-shaped pole pieces 31. In the present instance,'the pole pieces are attached to the magnet by screws 32, which also hold the magnet on the base 28. The diametric limbs 33 of the pole pieces carry a pair of coils 34', which are-connectedin seriesxand operate as asingle coil. .On the axiallimbs 35 of the pole pieces are mounted coils 36; The coils34 are adapted to be connected in a talking circuit, by which I mean any circuit of variable electric impulses that represent transmitted sound waves to be reproduced. The parallel limbsj35 of the pole pieces extend through holes 37 in housin 26 into operative relation to an armature dis or '42. The outer ture 38 remains firmly in adjuste bar 38 mounted on the a x of the diaphragm. As shown in Fi 3, t e armature is fixed to a rod 39 slide I mounted in a sleeve or hub 40 which may inte with a disk 41 secured to the diaphragm y screws or rivets ortion of rod 39 is screwthreaded, as indicated at 43, and a nut 44 is mounted on the screw-threaded end to permitadjustment of the armature 38 toward and away from the polar limbs 35. A fixed pin 45 in sleeve 40 engages in an axial slot 46 of rod 39 to prevent turning of the latter when the nut 44 is adjusted. A tensioned coil sprm 47 is arranged between armature 38 and sk 41 to hold the rod 39 pushed toward the electromagnetic unit, whereb the armaition.

- It will be understood that varia le current impulses in the circuit of coil or ils 34 produce a correspondingly variable magnetic effect on the armature 38 to cause vibration of the connected diaphra In the broad aspect of my invention, t e electromagnetic unit E may be regarded as representing any practical driving device for the diaph In the supportin head 13 of the rear panel 11 is mounted an e ectric generating unit indicated as a whole by G. In the casing 48 of unit G is fixed a permanent magnet 49 having pole pieces 50 on which are mounted a pair of coils 51, as best shown in Fig. 7.

The sounding board 14 carries an armature plate or disk 52 in operative relation to pole ieces 50. The cylindrical casing 48 is adustable in the fixed support 13 by a screwthreaded engagement 53. A suitable fingerpiece 54 projecting from the rear of the casmg permlts ready adjustment of the-normal airgap between pole pieces 50 and armature 52. If desired, a corrugated annular s ring 55 may be inserted to hold the unit G rmly in adjusted position without the possibility of rattling or working loose. It Wlll be clear from Fig. 7 that the vibrations of sounding board 14 cause the armature '52 to vary the magnetic field through the coil or coils 51, wherebyelectric impulses are generated in the circuit of these coils in accordance with the vibrations of'the sounding board.

. Theim ulses of generating unit G may be utilize in any practical way, but I refer to feed them'into the driving units E or the purpose of re-enforcing their action on the diaphragms. This will be understood from the-circuit diagram of Fig. 9. From the points 56 in the circuit of the generating Ill , tend no a h,or an other iece of a aratus inad for the rep'rodiibtion of 25nd. The current impulses generated in the circuit of coil or coils 51 b the vibratory movements of the sounding card 14 are sent through the parallel circuits 57 and 58into the auxiliary coils 36 of the driving units E, thereby re-enforcing or amplifying the electroma'gnetic effect of the'maino erating coils 34 on the-armatures 38 of the iaphragms. It will be understood, of course, that the coils 34 and 36 are so connected and arranged that their electromagnetic'eflectiscumulative. A variable inductance device 60 may be included in one or both of the generating circuits 57 and 58', so as to adjust the impedance value of each circuit for the most eflicient reproduction. That is to say, if we assume the diaphragms 19 and 20 to operate with greatest efliciency'at high notes and low notes res ectively, then the impedance of circuit 5 is so adjusted as'to transmit the higher frequencies more readily than the lower frequencies, while the impedance of circuit 58 is adjusted to transmit the lower frequencies most efficiently.

It will be seen from the preceding description that the sounding board 14 amplifies the reproduction in two ways: mechanically, by setting sound waves in motion; electrically, by generating current impulses that augment the electro-magnetic action of the driving units for the diaphragms. The armature 52 is so light that it adds no appreciable weight to the sounding board.

Although I have shown and described a specific construction, I want it understood that I have done so for the purpose of explaining the various features of my invention and not with the intent of imposing any restriction or limitation that is not included in the claims. It is to be expected that changes and modifications will occur to those skilled in the art without departing from the scope of the invention as defined in the following claims.

I claim as my invention: v

1. A loudspeaker comprising a trihedral A frame provided wit-h openings in two of its Walls, said frame being hollow to confine an open column of air wlthin its walls, a pair of loudspeaking diaphragms carried b said frame at said openings, whereby sai diaphragms. are directly exposed on one side to the outer air and on the reverse side to the open air column within said frame, and se arate electric means mounted on each of sai walls for operating said diaphragms, which cause vibration of said air column to reinforce the reproduction.

2. A loudspeaker comprising a trihedral frame provided with openings in two of its faces, a sounding board mounted on the third side of said frame, a pair of loudspeaking diaphragms carried by said frame at said 3, A, OUHSpeaRerlcomFriSing anlupright.

hollow em nating wa s that form a vertical sound chamber for confining a column of "air; said chamber being open at'the top, a loudspeaking diaphragm mounted in a Wall of said frame so as to be directly exposed on one side to the outer air and on the reverse side to said chamber, whereby said diaphragm vibrates the air column in said 'chamber to reinforce the reproduction, and electric means mounted on said wall for operating said diaphragm.

4. A loudspeaker comprising a 'hollow frame having walls that form a sound chamber for confining a column of air, said chamber being open at one end, one of said walls constituting a sounding board,a louds eaking diaphragm mounted in a wall of sai frame so as to be directly exposed on one side to the outer air and on the reverse side to said cham her and soundingboard, whereby said diaphragm causes'vibration of said sounding ard to amplify the reproduction, and an electric unit carried by saidfr'ame for operating said diaphragm.

5. A loudspeaker-comprising a trihedral supporting frame constructed to provide a sound chamber open to the outer air, a sounding board in said chamber, a loudspeaking diaphragm mounted on said frame so that the front of the diaphragm is directly exposed to the outer air and the rear of the dlaphragm is ex osed to said chamber and sounding boar and an electric driving unit carried by said frame for operating said diaphragm.

7. A loudspeaker comprising a direct-acting diaphragm, an electric driving unit for said diaphragm, said unit includin an electromagnetic coil, means mechanica 1y operated by sound waves produced by said diaphragm for generating current impulses in a circuit independent of the circuit of said coil, and means for causing said current impulses to reinforce the action of said coil.

8. A loud speaker comprising the combination .of a direct-acting diaphragm freely exposed to the'outer air, an electric driving unit for said diaphragm, a sounding board set in vibration by sound waves produced by I a current-generating device controlled by the said diaphragm, electromagnetic means operated by the movements of said sounding board to generate current impulses, and connections whereby said current impulses reinforce the actionof said driving unit on the diaphragm.

9. In an acoustic device, an electromagnetic driving unit comprising a substantially annular magnet structure provided centrally with a pair of L-shaped pole ieces in diametric alignment, each pole piece having a radial limb and an axial limb, the axial limbs terminating in polar faces, a pair of coils on said radial limbs, a separate pair of coils on said axial limbs, means associated with each;

pair of coils for generating electric impulses thereinin accordance with transmitted sound, and a diaphragm controlled by the combined action of said pairs of coils.

10. In an acoustic device, the combination of a diaphragm, an electromagnetic driving unit for said diaphragm, said unit comprising a magnet structure having a pair of pole pieces, two pairs of coils mounted on said pole pieces, one pair of-said coils being adapted,to be connected in a reproducing circuit, a vibratory acoustic member set in operation by sound waves produced by said diaphragm,

movements of said member, and means for connecting the other pair of said coils with said device to augment the electromagnetic effect of said driving unit.

11. In sound-reproducing apparatus, the combination of a pair of diaphragms having different natural frequencies for proper reproduction of high and low tones, an electromagnetic driving unit for each diaphragm, means for simultaneousl operating said driving units, a sounding oard set in vibration by the combined action of the sound waves produced by said diaphragms, electric means operated by the movements of said sounding board to generate current impulses, and a pair of parallel circuits between said electric means and said driving units for causing the impulses of said generating means to augment the electromagnetic action of said driving units.

12. A loudspeaker comprising a frame or casing constructed to form a sound chamber for confining a column of air, said chamber being open at one end, a plurality of loudspeaking diaphragms mounted on said frame so as to be directly. exposed on one side to the outer air and on the reverse side to said chamber, said diaphragms having different natural frequencies for the proper reproduction of high and low tones, and electric means carried by said frame for simultaneously operating said diaphragms, which cause the air column in said chamber to vibrate in accordance with the combined vibrations-of the diaphcii'agms, whereby the reproduction is amplifie 13. A loudspeaker comprising a hollow frame having walls that form a sound chamber for confining a colunm of air, said chamber being open at one end, one of said walls constituting a sounding board, a loudspeaking diaphragm mounted in a wall of said frame so as to be directl exposed on one side to the outer air and on t e reverse side to said chamber and sounding board whereby said diaphragm causes vibration of said sounding board to amplify the re roduction, an electric unit carried by said irame for operating said diaphragm, electric means operated by the movements of said sounding board to generate current impulses, and connections whereby said current impulses reinforce the action of said driving unit on the diaphra' m.

14. A loudspeaker comprising a trihe ral frame provided with openings 1n two of its faces, a sounding board mounted on the third side of said frame, a pair of loudspeaking diaphragms carried by said frame at said openmgs, whereby said diaphragms are directly exposed on one side to the outer air and on the other side to the open air column within said frame, so that said sounding board is set in vibration by said diaphragms to amplify the reproduction, electric driving units mounted on said frame for operating said diaphragms, electric means operated by the movements of said sounding board to generate current impulses, and connections whereby said current impulses reinforce the action of said driving units on the diaphragms.

15. In sound-reproducing apparatus, the combination of a pair of diaphragms having different natural frequencies for proper reproduction of high and low tones, an electromagnetic driving unit for each diaphragm, means for simultaneousl operating said driving units, a sounding card set in vibration by the combined action of the sound waves produced by said diaphragms, electric means operated by the movements of said sounding board to generate current impulses, a pair of parallel circuits between said electric means and said driving units for causing the impulses of said generating means to augment the electromagnetic action of said driving units, and a variable electric device in each parallel circuit to regulate its impedance value for the most efiicient operation of the connected diaphragm.

16. A loudspeaker comprising a trihedral frame constructed to' be self-supporting, a pair of loudspeaking diaphragms mounted on two walls of said frame, and electric drivmg means mounted on each of said walls for operating said diaphragms.

17. A loudspeaker comprising a hollow framework having walls adapted to confine an open column of air, a cone diaphragm mounted on a wall of said frame so as to be exposed on one side to the free air and on the reverse side to said confined column of air, whereby said diaphragm vibrates the air column to reinforce the reproduction, and an electric driving unit mounted onsaid framework for operating said diaphragm.

18. A- loudspeaker comprising a hollow frame having a Wall adapted to a'ctas a, sounding board, a cone diaphragm mounted on each of the other Walls, and electric means mounted on said frame for simultaneously operating said diaphragms, which cause said sounding board to vibrate and thereby augment the reproduction. 7 i

19. A loudspeaker comprising a trihedral frame having a Wall adapted to act as a sounding board a pair of loudspeaking diam phragms mounted on the other two Walls of, said frame, the vibrations of *said diaphragms setting said sounding board in operation to reinforce the reproduction, and electric driving means for simultaneously operating said diaphragms.

20. A loudspeaker comprising a supporting frame, a pair of direct-acting diaphragms mounted on said frame, said diaphragms having different natural frequencies so as, to reproduce the higher and lower musical registers, electric driving means for simultaneously operating said diaphragms, and a sounding board mounted on said frame so as to be set in vibration by the joint action of said diaphragms to reinforce the reproduction.

, 21. A loudspeaker comprising a hollow frame constructed to provide an open column of air, a cone diaphragm mounted on saidframe and exposed to said column of air to vibrate the same, a sounding board carried by said frame and set in operationby said column of air to reinforce the reproduction, and

speaking diaphragm, electromagnetic means including a coil for operating said diaoperating saiddiaphragm, a second diaphragm carried by said frame and arranged to be vibratedby sound Waves produced by said first diaphragm, and electromagnetic means for generating current impulses by the vibration of thesecond diaphragm, said frame providing a sound chamber of which said diaphragms constitute vibratory vvalls.

, a oLPH A. THOMAS;

electric driving means mounted on said frame for operating said diaphragm."

22. A loudspeaker comprising a hollow frame constructed to provide an open column of air, a cone diaphragm mounted on said frame and exposed to said column of air to, vibrate the same, a sounding board carried by said frame and set in operation bysaid column of air to reinforce the reproduction, electric driving means mounted on said frame for operating said diaphragm, and electromagnetic means operated by said sounding board to generate current impulses for reinforcing the electromagnetic action of Said driving means. 7

23. A loudspeaker, comprising a pan of direct-actmg dlaphragms having dliferent natural frequencies so as -to reproduce the higher and. lower musical registers, a sound v ing board set in operation by thesound waves produced by the combined action of sald diaphragms, electromagnetic mechanlsm for srmultaneously operating said diaphragms,

and electromagnetic means operated by said sounding board to generate current impulses for reinforcing said driving meehanlsm.

24. Acoustlc apparatus'comprismg a loud 

